A TZM alloy comprising 0.5% by weight of titanium (Ti), 0.07% by weight of zirconium (Zr), and 0.05% by weight of carbon with the balance consisting of molybdenum has hitherto been known as a molybdenum (Mo) alloy having improved high-temperature strength. In the TZM alloy, the melting point of molybdenum as the main component is high, and, thus, the TZM alloy has excellent high-temperature strength. The TZM alloy has been used in fields where high-temperature strength properties are required, for example, in X-ray tube rotary anode targets and melting crucibles for use in melting of metals and the like by taking advantage of this high-temperature strength property.
The use of the TZM alloy in X-ray rotary anode targets posed a problem that impurities in the alloy, such as oxygen, carbon, and hydrogen, are gasified and lower the degree of vacuum in the X-ray tube resulting in deteriorated properties of the X-ray tube. Likewise, melting crucibles using the TZM alloy also involve a problem that gas components emitted during melting disadvantageously contaminate the melt. For example, the TZM alloy has a problem that a gas component is evolved from the alloy in a service environment of a high temperature of, for example, 800° C. or above and 1200° C. or above.
In order to cope with the evolution of the gas component under such high-temperature conditions, for example, in Patent No. 3052240 (patent document 1) or Japanese Patent Laid-Open No. 279362/2001 (patent document 2), an attempt has been made to add titanium or zirconium as a carbide. Further, in patent documents 1 and 2, a method is adopted in which, after sintering of a molybdenum molded product containing the carbide added thereto in a hydrogen atmosphere, the sinter is then sintered in vacuo to reduce the carbon and oxygen contents of the molybdenum sinter. Japanese Patent Laid-Open No. 170510/2002 (patent document 3) discloses a molybdenum alloy in which a part of added titanium and zirconium has been brought to a composite oxide. All the molybdenum alloys disclosed in patent documents 1 to 3 have improved gas release properties and, thus, when used in the X-ray tube rotary anode target, emits no significant amount of gas components. Accordingly, X-ray tubes can be provided with a low rejection ratio.
Patent document 1: Patent No. 3052240
Patent document 2: Japanese Patent Laid-Open No. 279362/2001
Patent document 3: Japanese Patent Laid-Open No. 170510/2002